The present invention relates to pectins, to a process for their production, to acidic foods employing them and to a process for their production, and more specifically it relates to pectins obtained from root vegetables, and particularly tubers and corms, to a process for their production, to acidic foods such as acidic protein beverages obtained by adding citrus or other juices, organic acids or inorganic acids to protein beverages such as milk and soy milk, or acidic milk beverages, acidic frozen desserts and acidic desserts, as well as coffee beverages, lactic acid bacteria beverages, fermented milk, liquid yogurt and the like, and to a process for their production.
Root vegetables, and particularly tubers and corms, have long been known to contain starches and pectins (Ullmanns Enzyklopaedie der techn. Chemie, Bd. 13, 171, Urban and Schwarzenberg, Muenchen-Berlin (1962)), and they have been the subject of much research as production starting materials for pectins (Die Staerke 26 (1974) 12, 417-421, CCB 3, 1 (1978) 48-50, Getreide Mehl und Brot 37, 5 (1983) 131-137, Japanese Unexamined Patent Publication No. 60-161401, Chem. Eng. Technol. 17 (1994) 291-300, WO97/49298). Research has also been conducted in the past on their uses, mainly as gelling agents (ZSW Bd. 31 (1978) H.9 348-351, Getreide Mehl und Brot 37, 5 (1983) 131-137, WO97/49298).
As mentioned above, production of pectins from 35 tubers and corms has long been the subject of study as a research topic. However, in terms of its function as a gelling agent for jams and the like that has been examined as its major use, it has not excelled over pectin derived from fruits such as apples or citrus fruits, and its use has therefore not been practical to date. In addition, while uses and production processes for fruit-derived pectins have been investigated in depth, it is currently the situation that virtually no research has been carried out on the characteristic function of pectins obtained from root vegetables, and particularly tubers and corms, and on establishing the detailed production conditions.
For production of acidic protein foods it has been common in the past to use apple and citrus-derived pectins, water-soluble soybean polysaccharides, carboxymethylcellulose sodium, alginic acid propylene glycol aster and the like for the purpose of preventing agglutination and sedimentation of protein particles. However, for most stabilizers that are used, the pH range suited for satisfactory stabilization of protein dispersion is below the isoelectric point of the protein, and stabilizers have been desired which can stabilize acidic protein foods in a pH range above the isoelectric point.
On the other hand, it has been reported that protein components can be stabilized in the slightly acidic pH range from neutral to pH 5.2 by addition of organic acid salts (Japanese Examined Patent Publication No. 5-52170), but this technique entails problems such as loss of milkiness of the stabilized protein solution, and inability to achieve satisfactory acidity by the effect of the added organic acid salt.
In addition, milk proteins in acidic milk beverages such as liquid yogurt, lactic acid bacteria beverages or fruit milk are highly unstable and agglutinate, and time leads to sedimentation of the milk proteins and separation of the whey. Such agglutination occurs to a considerable degree during sterilization heating, resulting in total loss of product value.
Milk-added coffee that can be distributed at ordinary temperature has conventionally been made by mixing and dissolving raw materials such as coffee extract, milk components, sugars, emulsifiers and the like to make coffee compositions, and then subjecting them to a homogenizer and to a heating step at 110-135xc2x0 C. for sterilization either before or after being packed into storage containers; however, the high temperature of the heating step produces a decomposition reaction of the coffee components, and lowers the pH of the coffee solution. When the pH of the solution is lowered to acidity of under pH 6.0, the milk proteins in the milk components of the coffee solution are denatured, causing separation and agglutination, and destroying the product value. In order to prevent denaturation of the milk proteins, alkali substances such as sodium bicarbonate have been preadded to the coffee solution to adjust the pH of the coffee solution to above 6.5 before heating, but since the milk-added coffee produced by such methods is heated for sterilization at a pH of above 6.5, the coffee aroma is altered such that it exhibits the unique aroma and flavor of xe2x80x9cretort canned coffeexe2x80x9d, which is different from the original regular coffee.
On the other hand, there has been a strong demand for development of heat sterilized milk-added coffee beverages that can be stored at ordinary temperature and exhibit excellent acidic flavor, and as production methods for acidic milk component-added coffee beverages there have been proposed a method of using fresh cream or butter as the milk component and adding an emulsifier such as sucrose fatty acid ester and crystalline cellulose (Japanese Unexamined Patent Publication No. 6-245703) and a method of stabilizing the milk proteins using acidic polysaccharides (Japanese Unexamined Patent Publication No. 62-74241); however, neither of these methods has succeeded in stabilizing the milk components without impairing the unique flavor and properties of the coffee.
Thus, while coffee normally exhibits the characteristic flavor and acidity of regular coffee in the weakly acidic pH range of 6,5 and below, when the pH of the coffee solution is adjusted to above 6.5 during preparation the characteristic flavor and acidity of regular coffee is lost, and the coffee obtained by heat sterilization has therefore had greatly reduced flavor compared to the original regular coffee. That is no technique has existed allowing prolonged stabilization of milk components without impairing the flavor and properties characteristic of regular coffee.
Thus, although techniques have existed for stabilization of protein dispersion in the pH range below the isoelectric point and from pH 5.2 to neutral, no technique has existed allowing satisfactory stabilization of acidic protein foods in the general pH range of higher acidity than the isoelectric point of the proteins.
It is an object of the present invention to provide a pectin obtained by extraction from root vegetables and particularly tubers and corms and a process for its production, as well as acidic protein foods that are stable in the pH range above the isoelectric point of the proteins and a process for their production, and to provide heat sterilized milk-added beverages that can be distributed at ordinary temperature, wherein the milk components are stable for long periods. Here, xe2x80x9cacidityxe2x80x9d refers to the pH range of 6.5 and lower.
As a result of diligent research directed toward solving the problems described above, the present inventors have found that pectins obtained by hot water extraction under weakly acidic conditions from starch residue as a processing by-product of tubers and corms exhibit a characteristic function, and particularly that the use of potato-derived pectins can satisfactorily stabilize acidic protein foods in a pH range above the isoelectric point of the proteins at a lower viscosity than with fruit-derived pectins. Upon continued research subsequent to filing of Japanese Patent Applications No. 11-9984 and No.11-249464, it was further found that by using an emulsifier during extraction of the pectins it is possible to efficiently minimize or eliminate elution of starch contaminants in the starch residue. The present invention has been completed on the basis of these findings.
In other words, the invention relates to a process for production of pectins comprising adding an emulsifier during extraction of pectins from root vegetables and separating and removing the insolubles that are produced, as well as to pectins produced by the process, to a process for production of acidic protein foods comprising using the pectins, and to acidic protein foods produced by the process.
Examples of root vegetables as raw materials for extraction of pectins according to the invention include tubers and corms such as potatoes, sweet potatoes, taros, yams and devil""s tongue root, as well as burdocks, carrots, radishes, lotus roots, beets and the like, among which tubers and corms are particularly preferred. Such tubers and corms can be used either in raw or dried form, but preferably the raw or dried starch residue produced as a processing by-product of starch industry is used, and such starch residue from potatoes is readily available.
The extraction of pectins from the raw material is preferably carried out under weak acidity from pH 3.8 to pH 5.3. Pectins extracted outside of this pH range tend to not as easily exhibit a dispersion stabilizing function for proteins in the pH range above their isoelectric points.
Incidentally, while the reason why pectins extracted in this pH range exhibit the function described above is not completely understood, it is believed that the degree of esterification of the polygalacturonic chains in the extracted pectins and the stereostructure of the neutral sugar chains are probable contributing factors.
The pectin extraction temperature in the aforementioned pH range is preferably 100xc2x0 C. or above. When the extraction is carried out at a temperature below 100xc2x0 C., time is required for elution of the pectins and the process is economically unfeasible. On the other hand, while extraction is completed in a shorter time with increasing temperature, an excessively high temperature will have an adverse effect on the flavor and color while also promoting low molecularization of the pectins, thus lowering the function-exhibiting effect, and therefore the extraction is preferably carried out at no higher than 130xc2x0 C.
The pectins according to the invention exhibit an even stronger effect if the contaminating starch is Am maximally removed to increase the purity. (The contaminating starch is preferably no greater than 60% and more preferably no greater than 50% as the content measured by quantitation using iodine.) The starch may be removed by, for example, decomposition with enzymes, washing removal from the raw material with water at 100xc2x0 C. or below, or separation of the insoluble portion in the extract; according to the invention, however, using an emulsifier allows removal of the starch in an easy and effective manner. Specifically, an emulsifier is added to the extracted raw material solution for insolubilization of the starch, so that the insoluble portion can be separated and removed from the extract. Thus, it may also be accomplished by adding the emulsifier to the pectin extract after extraction of the pectin and separating and likewise removing the insolubilized portion with means such as a centrifugal separator, and the emulsifier may be added at any stage during, before or after extraction of the pectin. Pectin with any molecular weight value may be used, but it preferably has an average molecular weight of a few tens of thousands to a few million, and specifically from 50,000 to 300,000. The average molecular weight of the pectin is the value determined by the limiting viscosity method whereby the viscosity is measured in a 0.1 molar NaNO3 solution using standard pullulan (Showa Denko Co., Ltd.) as the standard substance.
The emulsifier used for the invention preferably has a hydrophilicity with an HLB value of 5.5 or greater, and more preferably an HLB value of 10-19.
The emulsifier used for the invention also preferably has a hydrophobic fatty acid carbon chain length of C12 or greater. Specifically, the carbon number of the main constitutional fatty acid of the emulsifier is preferably 12-26.
The amount of emulsifier used may be 0.2-10 wt % and preferably about 0.5-5 wt % based on the solid (for example, starch residue) of the extracted raw material as a general standard, but since this may vary according to differences in the starch concentration, the amount used does not restrict the scope of the invention.
The pectins derived from root vegetables and particularly tubers and corms, which are obtained according to the invention, have a characteristic function differing from conventional pectins derived from fruits such as apples and citrus fruits. Specifically, whereas fruit-derived pectins are used as stabilizers for acidic milk beverages by utilizing their function that can stabilize dispersion of proteins in a pH range below their isoelectric point, the pectin according to the invention has a function that can stabilize dispersion of proteins in a pH range above the isoelectric point, and this function allows production of acidic protein foods that are stable in a pH range above the isoelectric point, which have not been obtainable by the prior art.
An acidic protein food according to the invention is an acidic food containing animal or vegetable protein, and the term includes acidic protein foods such as acidic protein beverages obtained by adding citrus or other juices, organic acids such as citric acid or lactic acid or inorganic acids such as phosphoric acid to protein beverages containing animal or vegetable proteins, such as milk and soy milk, acidic milk beverages obtained by acidifying dairy products, acidic frozen desserts such as acidic ice cream, frozen yogurt and the like obtained by adding fruit juice to frozen desserts containing milk components such as ice cream, acidic desserts obtained by adding fruit juice or the like to gelled foods such as puddings and Bavarian cream, as well as coffee beverages, lactic acid bacteria beverages (including live bacteria and pasteurized types) and fermented milk (solid and liquid types). Animal or vegetable proteins include cow milk, goat milk, skim milk, soybean milk, and whole milk powder or skim milk powder obtained by powdering these, as well as sugar-added milk, condensed milk, processed milk obtained by fortification with minerals such as calcium or vitamins, fermented milk, and the proteins obtained from the same. Fermented milk refers to fermented milk obtained by addition of a lactic acid bacteria starter and fermentation after sterilization of the animal or vegetable proteins, and it may be further powdered sugar may be added thereto as desired.
The amount of pectin used for the invention may be 0.05-10 wt % and preferably about 0.2-2 wt % based on the final product as a general standard, but since this may vary according to differences in the protein concentration, the amount used does not restrict the scope of the invention.
For production of an acidic protein food according to the invention there may also be used in combination conventional stabilizers such as apple and citrus-derived pectins, water-soluble soybean polysaccharides, carboxymethylcellulose sodium, alginic acid propyleneglycol ester, carrageenan, fine crystalline cellulose, chitosan, organic acid salt, heavy phosphoric acid salts, emulsifiers, heat-denatured proteins and the like, which can increase the stable pH range.